Concentration of phosphatic material



United States Patent CONCENTRATION OF PHOSPHATIC MATERIAL Clinton A. Hollingsworth and Jordan L. Wester, Lakeland, Fla., assignors to Smith-Douglass Company, Incorporated, Norfolk, Va., a corporation of Virginia No Drawing. Application July 15, 1954, Serial No. 443,693

4 Claims. (Cl. 209166) This invention relates to the froth flotation process for concentrating phosphatic material and more particularly to the separation of silica from phosphatic material by froth flotation, and has for its object the provision of an improved method of froth flotation for separating silica from phosphatic material.

The main phosphatic constituent of Florida phosphate rock, as well as most native phosphate rocks containing fluorine, is fluorapatite (usually referred to as apatite) commonly believed to be a combination of tricalcium phosphate and calcium fluoride (Ca1oF2(PO4)6). The grade of the rock is determined by its tricalcium phosphate content, which is usually designated in the industry as bone phosphate of lime (BPL). Silica is one of the chief valueless or gangue constituents of phosphate rock and in the phosphate industry is commonly determined and reported as insolubles (InsoL). For many purposes, such as the defluorination of phosphate rock by calcination without fusion, a phosphatic raw material of good grade and low silica content, say less than 4% and preferably not exceeding 3% insol., is desirable.

In the washing and concentration of phosphate rock, it is presently the common practice throughout the Florida phosphate field to double float phosphate. That is, after rough concentration by washing and the like, final concentration is effected in two stages of froth flotation. In the first stage, a deslimed flotation feed of the raw rock is conditioned with caustic soda, fuel oil and a fatty acid such as tall oil, and the conditioned feed is subjected to froth flotation where a phosphate product (commonly called a rougher concentrate) is floated and the underflow (largely silica) is discarded to waste. The rougher concentrate normally contains 8 to 20% of silica, and hence its phosphate grade (BPL) is too low to be of much practical value. Accordingly, the rougher concentrate is de-oiled by scrubbing with sulphuric acid followed by desliming. The de-oiled product (commonly called the amine cell feed) is subjected to the second stage of froth flotation in the presence of a strong cationic collecting agent, such as an amine, where silica is floated and discarded to waste. The underflow of the second stage of flotation is a high grade phosphate product, and is transferred to storage. In the phosphate field, the phosphate product is called the concentrate regardless of whether it is the floated product or the underflow, and hence the silica float is called tailings (tails).

Phosphate ores are friable and tend to produce deleterious amounts of slime during flotation treatment, especially in machines of the agitation type. Slime has been found to be particularly objectionable in the amine circuit flotation, since the presence of slime necessitates an increased amount of the relatively costly amine reagent with an attendant loss of phosphatic material in the silica tailings in order to obtain the desired low silica content in the phosphate concentrate. The aim of the present invention is to provide an improved method of separating silica, as a float, from phosphatic material by froth flotation in the presence of a cationic collecting flotation agent more selective with respect to silica than the cationic collecting agents of the amine type heretofore available and used in the phosphate field. Thus, by the practice of the invention increased recovery of phosphatic material is attained and a phosphate concentrate of low silica content is obtained without an undue loss of phosphatic material in the silica tailings. i

The commercially available amine flotation agents are usually made from higher fatty acids derived from animal and vegetable oils, and in the trade are commonly called fatty amines. Chemically, these commercial fatty amines are usually normal aliphatic amines, or mixtures thereof, whose alkyl groups contain 8 to 22 carbon atoms, such, for example, as n-octyl-, n-decyl-, n-dodecyl-, n-tetradecyl-, n-hexadecyl-, n-octadecyl-, octadecadienyl-amine, or the water-soluble acetate salts of such amines. Since nitriles are intermediate products in the manufacture of the fatty amines, it is frequently the practice to market amine flotation agents with some unconverted nitrile content, say around 30%. The sulphate salts of the fatty amines are insoluble in water and cannot be readily emulsified or dispersed in an aqueous medium, and probably on these accounts have heretofore been considered useless as cationic collecting agents.

We have discovered that when one of the commercially available fatty amine productsis reacted with a limited amount of concentrated sulphuric acid in the presence of a substantial proportion of kerosene, or equivalent liquid hydrocarbon, the resulting reaction product is an effective cationic collecting agent possessing greater selectivity for silica than does the unreacted fatty amine product. Thus, we have found that when the fatty amine product is mixed with the kerosene, it is possible to add a limited amount of concentrated sulphuric acid to the mixture without solidification of the reaction product. The resulting reaction product can be readily emulsified or dispersed in water and possesses greater selectivity for silica and has less tendency to float phosphate, in the separation of silica from the phosphate by froth flotation, than the untreated or unmodified amine product. Based on those discoveries, the present invention involves subjecting a phosphatic material containing silica to froth flotation in the presence of the reaction product .of concentrated sulphuric acid and a mixture of a fatty amine with a liquid hydrocarbon.

While we are unable to explain the exact nature of the chemical reaction that takes place in preparing the reaction product, we believe that the sulphuric acid reacts to modify the amine, although the limited amount of sulphuric acid present in the reacting mixture is considerably less than the stoichiometric quantity required to theoretically convert all of the amine to its sulphate salt. Moreover, the reaction product, with its modified amine constituent, is an effective cationic collecting flotation agent, whereas the sulphate salts of the fatty amines have been considered useless as flotation reagents. The function of the liquid hydrocarbon is not clearly understood, but We believe it acts both as a solvent or disperser of the amine and as a diluent. While a light hydrocarbon fuel oil like kerosene is now preferred as the amine solvent, the amine may equally well be dissolved or dispersed in other liquid hydrocarbons, such as turpentine, pine oil and other terpenes, light petroleum fuel oils, and aromatic hydrocarbons like benzene and toluene.

In preparing the reaction product, the fatty amine is mixed with the liquid hydrocarbon in the proportions of from 1 to 10 parts by weight of liquid hydrocarbon for each part of free fatty amine, the preferred relative proportions being from 2 to 6 parts of liquid hydrocarbon for each part of free fatty amine. The amine-liquid hydrocarbon mixture should contain at least 50% by weight of the liquid hydrocarbon, and preferably around since with too little liquid hydrocarbon the reaction product is solid or too thick or viscous to be efficiently handled as a flotation agent. The source of the fatty amine may conveniently be one of the commercially available fatty amine flotation products containing at least 70% of free fatty amine, and the free fatty amine content of the commercial product may conveniently be considered as 100% in calculating the relative proportions of liquid hydrocarbon and free fatty amine in the mixture. Thus, using such a commercial product as the source of the fatty amine, from 50 to by weight of the commercial product are mixed with from 50 to 90% of the liquid hydrocarbon, the preferred proportion of liquid hydrocarbon in such a mixture being from 65 to 85%, and more particularly about 80%.

Concentrated sulphuric acid (Le. 93 to 99% HzSO-z) is slowly added to the amine-liquid hydrocarbon mixture while continuously stirring, in the proportions of from 0.1 to 0.6 part by weight of acid (calculated as H2804) for each part of free fatty amine, and preferably from 0.14 to 0.25 part of acid ,per part of amine. Concentrated sulphuric acid is required because the presence of water in the reacting mixture tends to form a dense, milky, emulsion-like reaction product, which is diflicult to handle. Preferably, the sulphuric acid is added to the amine-liquid hydrocarbon mixture over a. period of at least 30 minutes. The resulting reaction product is fluid and stable under normal atmospheric conditions.

The following examples illustrate various practices of the method of the invention and the technical and economic advantages thereof. In the tables of all examples (unless otherwise noted), the column headed H2804 indicates the parts by weight of sulphuric acid (calculated as H2804) added to a mixture of parts by weight of a commercial fatty amine flotation product and 80 parts by weight of kerosene.

amine is the parts by weight of sulphuric acid per part of free fatty amine (or the equivalent thereof when the amine has been acetylated) added to the mixture. The tables give the BPL and Insol. (SiOz) contents of the concentrate, the percent of BPL lost in the silica tails, the percent of BPL recovered in the concentrate, and the tons of concentrate per 100 tons of feed. Unless otherwise noted, the 'feed was a commercial amine cell feed of the following chemical and screen analyses:

Chemical analysis The flotation reagent used in the first test of each table was the unmodified mixture of 20 parts of commercial amine product and parts of kerosene (as a standardof comparison), and in each subsequent test of that table an equivalent amount of amine per ton of feed was used as the flotation agent in the form of the reaction product. The feed was conditioned with the reagent at about 20% solids for about 5 seconds in a laboratory Fagergren flotation cell (air valve off), after which the air valve was opened, the conditioned feed was subjected to a froth flotation operation, the silica float (tails) was removed by hand skimming, and a phosphate concentrate of .low

4 silica content was recovered in the underflow of the froth flotation operation. All flotation conditions were kept constant, and unless otherwise noted, the only variable was the amount of sulphuric acid added to the mixture of kerosene (or other liquid hydrocarbon where noted) and fatty amine in preparing the reaction product.

EXAMPLE I The reaction product was prepared from a commercial amine product (Armour and Co.s Armoflote S) consisting of about 70% free fatty amine and about 30% nitrile, and the froth flotation operation was carried out in the presence of the equivalent-of 0.276 pound of the amine product per ton of feed.

The reaction product was prepared from a commercial amine product (American Cyanamid Companys S- 2026) consisting of a partially acetylated fatty amine made up of about 94-95% amine and about 45% acetic acid, and the froth flotation operation was carried out in the presence of the equivalent of 0.254 pound of the amine product per ton of feed.

- mine BPL, InsoL, Tails Rec. '1. F

Percent Percent i 74. 95 2. 61 21. 29 97. 0 9o. 3 1.11 0. 076 74. 97 2. 56 20. 39 97. 2 so. 4 l 2. 44 0.132 74. 911 a. 1.1 .12. .07 98. 5 211. 7 E a. 23 0. 176 75. 06 a. 12 10. 29 98.8 91. 7

3.85 0.211 74. '3. 10 M3 98.0 112. -1 4. 76 11.263 74.90 3.35 9. as es. 9 92:1

EXAMPLEIII The reaction product was prepared froma commercial amine product (Armour and Cois .Armac T") consistingof an acetylated fatty amine made up ofabout 84.5 amine and about 15.5% acetic acid, and the froth flotation operation was carried=out in the presence of the equivalent of "0.329 pound of the amine product per ton of feed.

Cone. P Y P 1 O 1 I ereent crcent, i rnso. 31 L411. .BPL per 10 Amine B-PL, InsoL, Tails Rec. T. 'F. 'Pmcuut P8100110 l 75.09 :2.7s 15.76 98.0 i 91.0 i 0. 90 0. 76.27 2.07 27.46 94.7 86.6 K 2. 05 0. 161 75:43 2.48 -10. 20 '98; 7 01. 2 8.32 0.537 74.92 2. 11.22 99. 1 2122. s 9. 82 0645 75722 2.54 I 14.59 98.1 90.9 l 11.28 0. 753 1 '757'47- 2.41 V 24.19 06.1 883 I 1 EXAMPLE'IV The reaction .product was prepared from acommercial amine product (General Mills :Inc.s fSpecial Alamine tRC v2665) consisting of a substantially 100% .free .fatty 75 amine, and'theifroth dlotation operation was carried-out inthe presence of the equivalent of about '0.2'pound of the amine product per ton of feed.

Cone. H23 04 Percent Percent T. C H180 BPL in BPL per 100 Amine BPL, Insol., Tails Rec. T. F.

Percent Percent EXAMPLE V The reaction product was prepared from a commercial amine product (Armour and Co.s Armeen T) consisting of a substantially 100% free fatty amine, and the froth flotation operation was carried out in the presence of the equivalent of 0.336 pound of the amine product per ton of feed. In preparing the reaction product, the indicated amounts of sulphuric acid were added to a mixture of of the commercial amine product with 85% of kerosene.

Cone P P C ercent erccnt mso. 9 BPL in 'BPL per 100 Amme BPL, Insol., Tails Rec. F.

Percent Percen EXAMPLE VI In the tests of this example, the reaction product was prepared from the commercial amine product used in Example I (Armoflote S), and 20 parts of the amine product were mixed with 80 parts of crude turpentine. To this mixture, the indicated amounts of sulphuric acid were added to prepare the reaction product, and the froth flotation operation was carried out in the presence of the equivalent of 0.273 pound of the commercial amine product per ton of feed.

Cone. Hugo1 Percent Percent T. 0. H280 BPL in BPL per 100 Amine BPL, Insol., Tails Rec. '1. F.

Percent Percent EXAMPLE VII The tests in this example were conducted under the same conditions as in Example VI with the exception that in preparing the reaction product 20 parts of the commercial amine product (Armoflote S) were mixed with 80 parts of pine oil.

In the tests of this example, the reaction product was 75 prepared from the commercial amine product used in Example I (Armoflote S), and 20 parts of the product were mixed with 80 parts of benzene. To this mixture, the indicated amounts of sulphuric acid were added to prepare the reaction product, and the froth flotation operation was carried out in the presence of the equivalent of 0.19 pound of the commercial amine product per ton of feed. The

chemical analysis of the amine cell feed was 68.95% BPL and 9.88% Insol. 10

O onc.

Percent BPL in Tails Percent BPL, Percent Insol.

15 Percent amine the relative proportions by weight of kerosene to free fatty amine in the amine-kerosene mixture ranged from 9:07 to 40:42.

Reagent Composition Percent L in Tails H28 0 Amine Reagent lb./T. Feed Percent Percent g AHL Percent Prod.

Percent Kero.

EXAMPLE X Y The froth flotation operations in this example were continuous operations of at least two weeks duration each in a commercial flotation plant with regular amine cell feed. The first test (1953 Comp) is the composite result obtained during the year 1953 in the same plant using a commercial amine flotation product. In tests A, B and C, the reaction product was prepared by mixing 20 parts of the commercial amine product with parts of kerosene, and sulphuric acid was added to the mixture in varying amounts as indicated by the HzSO4 to amine ratio. The last column in the table gives the tons of concentrate per hour left in the silica float tailings, and shows that '7 only'about 2 tons of concentrate-per hour were lost when the froth flotation operation was-carried out in the presence of the reaction product, contrasted with the heretofore loss of 11 tons of concentrate per hour when the considerably in excess of the amount floated-with the'silica where the reaction product waspreparedwith the H 60 amine froth flotation operation was carried out in the presence 5 i h i c0ntemp1ate of an unmodified commercial amine product. Generally, the method ofthe invention efiects an im- Feed Concentrate H430 Percent Percent TO/Hr. Amine BPLni BPL leicin BPL, 111501., BPL, InsoL, Tails Rec. Tails Percent Percent Percent 'Percent 1953 Comp 71.13 10.12 76.48 4.42 45.97 88.6 11.0 A o. 20 68. 45 13. 73 75. a9 4. 2s 22. 09 95.6 4. i 0. 18 70. 9? 10. 75 76.63 4.32 19. 76 97. 2 2. 0 0. 71.81 s. so 76. 46 a. s1 19. 02 97. a 2; 0

Commercial fatty amine flotation products are comproved recovery of phosphatic material. This results monly made from tallow, cottonseed oil, soybean oil, 20 mainly from the greater selectivity for silica ofthe reaccoconut oil and the like, and hence ditferent commercial tion products. Thus, the loss of'phosphate iii the silica products have somewhat difierent characteristics. For float tails is substantially less than heretofore commonin this reason, in preparing the reaction product, optimum the Florida phosphate field. 'At'the-same time the phosresults are frequently obtained by using. slightly different phate concentrate is of satisfactory grade and of low amounts of sulphuric acid with diiferent amine products. as silica content. In addition to the economic advantage We have examined most of the commercially available resulting from the improved recovery of phosphatic maamineproducts, and have found that an addition of sulterial, the cost of the flotation reagent in the method of phuric acid (to the amine-liquid hydrocarbon mixture) the invention is generally less than in the amine circuit ranging between about 0.10 part of acid. per 1 part of flotation practices of the prior art. amine to about 0.60 part of. acid per 1 part of amine We claim: gives a reaction product having improved properties as 1. The method of separatingsilica from a mixture of a cationic collecting flotation agent. Sulphuric acid adphosphatic material and silica, which comprises subjectditions (to the amine-liquid hydrocarbon mixture) above iug the phosphate-silica mixture to a froth flotation about 0.60 part of acid per 1 part of amine generally yield Operation in the presence of a cationic collecting flotareaction products of inferior quality as cationic flotation tion agent consisting of the reaction product of conagents. In our present plant practice, the preferred acid centrated sulphuric acid and a mixture of a fatty amine to free amine ratio with a liquid hydrocarbon, the mixture consisting of H280 about 1 part by weight of amine per 4 parts of liquid m hydrocarbon and from 0.14'to 0.25 part by weight of 40 sulphuric acid (calculated as H2804) being. reacted with is about 0.143. each part of amine in the mixture, and recovering a Most of the commercial fatty amine flotation products phosphate cgncentrate in h d fl f the fl ti which we have examined, even when mixed with a large operation hi o flo i a silica fl t amQuHt 0f kerosene equivalent liquid hydrocarbon), 2. The method of separating silica from a mixture of solidify uP011 the additiml t0 the miXiure of all ammmt of 5 phosphatic material and silica, which comprises subjectslllphuriii acid approaching the PP limit of our ing the phosphate-silica mixture to a froth flotationv opera- H2804 tion in the presence of a cationic collecting flotation amine agent consisting of the reaction product of concentrated u sulphuricacid and a mixture of a fatty amine with a ratio (about Anflofiote S 15 the only except)? liquid hydrocarbon, the relative proportions by weight we have found but reaction products prepared from this of liquid hydrocarbon and fatty amine in the mixture commerclal amme Prodct wlth an being respectively between. 1:1 and 9z-l-and from 0.1 H 30 to 0.6 part by weight of sulphuric acid (calculated as m H2504) being reacted with-each part of fatty amine in the mixture an eco erin e I do .h. in plant practice. Table III illustrates, in the 2nd and a Silica float. last two tests the results obtamed Wlth 3'. The method of separating silica from a mixture of H 80 .phosphatic material and silica, which comprises subjectamine 0 ing the phosphate-silica mixture to a' froth: flotation opratios lower and higher, respectively, than herein conemmm m F presnce canon: t l i flotauon agent consisting of the pioduct ofthe reaction of contemplated in preparing the reaction product. Considerad 1 h t p p f f H tion of these tests shows that the reaction products emceimrate. 9 am 'i .amlx We a y with a light petroleum fuel oil, the relativeproportions ployed therein possessed no better selectivity for. silica b ht ht t l f 1 d f H than the unmodified commercial amine product. In the a 9 2 pc to f an g last two tests of Example V, the reaction product was t e mlxtme respective) .etween I preparedwith an and from 0.1 to 0.6 part by weight. of sulphuric acid (calculated. as H2504) being reacted with each part of 2 4 fatty amine in the mixture, and recovering a phosphate amine concentrate in the underfiow of the flotation operation ratio. exceeding that herein contemplated, and it will be observed that the resulting reaction products did not possess any better selectivity for silica than the unmodified commercial amine product. The amount of phoswhile overflowing a. silica float.

4. The method of. separating silica from a mixture ofphosphatic material and silica, which comprises subjecting the phosphate-silica mixture. toa forth flotation opphate floated in the silica tails of these. two tests was erat on in the presence of a cationiecollecting flotation 9 10 agent consisting of the product of the reaction of conmixture, and recovering a phosphate concentrate in the centrated sulphuric acid upon a mixture of a fatty amine underfiow of the flotation operation while overflowing with a light petroleum fuel oil, the relative proportions a Silica float. hy weight of light petroleuni fuel oil and fatty amine References Cited inthe file of this patent In the mixture being respectively between 2:1 and 6:1, 5 and from 0.14 to 0.25 part of sulphuric acid (calculated UNITED STATES PATENTS as H2804) being reacted with each part of amine in the 2,222,728 Tartaron et al Nov. 26, 1940 

1. THE METHOD OF SEPARATING SILICA FROM A MIXTURE OF PHOSPHATIC MATERIAL AND SILICA, WHICH COMPRISES SUBJECTING THE PHOSPHATE-SILICA MIXTURE TO A FROTH FLOTATION OPERATION IN THE PRESENCE OF A CATIONIC COLLECTING FLOTATION AGENT CONSISTING OF THE REACTION PRODUCT OF CONCENTRATED SULPHURIC ACID AND A MIXTURE OF A FATTY AMINE WITH A LIQUID HYDROCARBON, THE MIXTURE CONSISTING OF ABOUT 1 PART BY WEIGHT OF AMINE PER 4 PARTS OF LIQUID HYDROCARBON AND FROM 0.14 TO 0.25 PART BY WEIGHT OF SULPHURIC ACID (CALCULATED AS H2SO4) BEING REACTED WITH EACH PART OF AMINE IN THE MIXTURE, AND RECOVERING A PHOSPHATE CONCENTRATE IN THE UNDERFLOW OF THE FLOTATION OPERATION WHILE OVERFLOWING A SILICA FLOAT. 